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So now WhatsApp is finally on par with iMessage and Signal, and shares the same weakness: public key distribution. Key distribution is controlled by a centraliz

by aorth 11y ago

So now WhatsApp is finally on par with iMessage and Signal, and shares the same weakness: public key distribution. Key distribution is controlled by a centralized server that could, for malicious or other reasons, send you new fake keys for people you communicate with. For iMessage, this is explained in this 2015 post by Matthew Green: http://blog.cryptographyengineering.com/2015/09/lets-talk-about-imessage-again.html http://blog.cryptographyengineering.com/2015/09/lets-talk-ab... At least with Signal you can compile your own client (though that doesn't help if the server is going to send you fake public keys!).

x1798DE 11y ago
Is there no UI notifying you that a user's keys have changed in Signal? If so, the central server would need to send compromised keys on day 1, which would be detectable when you check the key signature.
- aorth 11y ago
  There is a UI. It doesn't even show (decrypt) the new messages until you add the new key.
TillE 11y ago
If you go to Settings -> Account -> Security, you can enable the option that will notify you in case the key changes. You do have to trust the client and opt in, but the feature exists.
- aorth 11y ago
  You're right. So when you get a notification of a key change (for malicious or other reasons) it is up to you to verify that the user did indeed have a key change — preferably out of band, or at least over another medium.